Workmanager заканчивается время, которое я ему установил

Question

Я использую workmanager для отправки уведомлений каждые 15 минут.Это мой код:

class UpdateWorker(context : Context, params : WorkerParameters)
    : Worker(context, params) {

    override fun doWork(): Result {

        // Do the work here--in this case, compress the stored images.
        // In this example no parameters are passed; the task is
        // assumed to be "compress the whole library."

        sendNotification("WorkManager", "EL work manager funciona.")

        // Indicate success or failure with your return value:
        return Result.success()

        // (Returning Result.retry() tells WorkManager to try this task again
        // later; Result.failure() says not to try again.)

    }

    fun sendNotification(title: String, message: String) {

        Log.e("Work manager", "Sync");

        val notificationManager = applicationContext.getSystemService(Context.NOTIFICATION_SERVICE) as NotificationManager

        //If on Oreo then notification required a notification channel.
        if (android.os.Build.VERSION.SDK_INT >= android.os.Build.VERSION_CODES.O) {
            val channel = NotificationChannel("default", "Default", NotificationManager.IMPORTANCE_DEFAULT)
            notificationManager.createNotificationChannel(channel)
        }
        val notification = NotificationCompat.Builder(applicationContext, "default")
                .setContentTitle(title)
                .setContentText(message)
                .setSmallIcon(R.mipmap.ic_launcher)
        notificationManager.notify(1, notification.build())
    }

}

В MainActivity:

//work manager
    val myConstraints = Constraints.Builder()
            .setRequiredNetworkType(NetworkType.CONNECTED)
            // Many other constraints are available, see the
            // Constraints.Builder reference
            .build()

    val updateWork = PeriodicWorkRequest.Builder(UpdateWorker::class.java, 15, TimeUnit.MINUTES)
            .setConstraints(myConstraints)
            .build()

    WorkManager.getInstance().enqueue(updateWork!!)
//end workmanager

Что происходит, я не понимаю, почему, если я укажу, что уведомление отправляется каждые 15 минут, ононе показано в то время.Посмотрите журнал времени, в которое он показан:

02-07 16:30:11.371 3763-3789/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:33:10.831 3763-3818/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:38:49.611 3763-3789/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:38:49.631 3763-3818/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:38:49.651 3763-3789/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:38:49.661 3763-3818/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:38:49.671 3763-3789/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:38:49.681 3763-3818/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:38:49.701 3763-3789/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:38:49.711 3763-3818/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:38:49.731 3763-3789/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:38:49.751 3763-3818/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:40:50.041 3763-3789/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:43:55.861 3763-3818/cu.uci.cegel.quejas E/Work manager: Sync
02-07 16:45:11.441 3763-3789/cu.uci.cegel.quejas E/Work manager: Sync